This invention pertains to boron thermal regeneration systems, and more particularly to an ion exchanger for such a system and a method for operating same so as to allow rapid changes in the boric acid concentration in the reactor coolant system for load follow operations.
Presently contemplated chemical shim nuclear reactor systems will use ion exchangers to store or release an amount of borate ions which correspond to the change in boric acid concentration in the reactor coolant system during a load follow operation. The process removes boric acid from the reactor coolant system after a load reduction and stores it on the ion exchangers at relatively low temperatures. When needed, the stored boric acid can be returned to the reactor coolant system by raising the temperature of the anion exchangers. Because the amount of resin in the system is sized to accommodate the maximum required changes, the resin will therefore become saturated at the new temperature level after only a maximum change in concentration. For smaller changes in the reactor coolant boron concentration, the resin bed will not become completely saturated. Incomplete saturation of the resin results in a slow response of the system, after a change in operating temperatures of the resin, which makes the system unsuitable to follow load cycles other than the specific cycle for which it was designed.
In accordance with the prior art, dilution of the boric acid concentration in the reactor coolant was accomplished by sending the let-down flow, at relatively low temperatures, to the thermally regenerable ion exchangers. The water loses its content of boric acid which becomes stored on the resin. Water haivng a low concentration of boric acid thus leaves the ion exchangers and is sent back to the volume control tank from which the existing charging system returns the water to the reactor coolant system. The boration flow path through the ion exchanges was the same as during the dilution operation except that the temperature of the flow sent to the thermally regenerable ion exchangers was at a higher level. The water flowing through the ion exchangers would remove boron from the resins and the boron enriched water was returned to the reactor coolant system via the volume control tank and charging pumps.
The difficulty with the undirectional flow system of the prior art, as described above, was that the system was of extremely slow response where incomplete saturation of the resins resulted from a previous change in boron concentration. The system was thus unsuitable to follow loads other than load follow operations resulting in equilibration at a saturation level for the column. Moreover, this problem could not be solved by simply allowing flow reversal within the usual vertical column resin bed since a migration of the particles due to separation of the bed on flow reversal would make the results of any particular temperature change extremely unpredictable.